This invention relates to the conversion of heat energy into electrical energy utilizing a hydrogen electrochemical cell.
The conversion of chemical energy to electrical energy may be accomplished in a variety of ways. It is known that electrochemical cells or batteries rely on redox reactions wherein electrons from reactant being oxidized are transferred to a reactant being reduced. With the separation of the reactants from each other, it is possible to cause the electrons to flow through an external circuit where they can be used to perform work.
Electrochemical cells however have had a problem related to the exhaustion of the reactants. Although most cells can be recharged by applying a reverse polarity voltage across the electrodes, such recharging requires a separate electrical source. During the recharging of the cell the cell typically is not utilized as an electrical power source, thus rendering it unusable during the recharging period.
Fuel cells have been developed in an effort to overcome problems associated with electrochemical cells. Typically, fuel cells operate by passing an ionized species across a selective electrolyte which blocks the passage of the non-ionized species. By placing porous electrodes on either side of the electrolyte, a current may be induced in an external circuit connecting the electrodes. The most common type of fuel cell is a hydrogen-oxygen fuel cell which passes hydrogen through one of the electrodes while oxygen is passed through the other electrode. The hydrogen and oxygen combine at the electrolyte-electrode interface to produce water. By continuously removing the water, a concentration gradient is maintained to induce the flow of hydrogen and oxygen to the cell.
These types of fuel cells however suffer from a number of disadvantages. These cells must be continuously supplied with a reactant in order to continuously produce electricity. Additionally, these cells produce a continuous product stream which continuously must be removed, the removal of which may pose a problem. The porous electrodes of these fuel cells must allow the passage of the reactant entering the cell. However, over time these porous electrodes can become fouled or plugged so as to slow or even prevent the passage of the reactant. Such slowing of the reactant flow reduces the production of electricity. Lastly, the selection of an appropriate electrolyte is not always easy. The electrolyte must rapidly transport the ionized species in order to increase the current production. Frequently, the limited migration of the ionized species through the electrolyte is a limiting factor on the amount of current produced.
In an effort to avoid the problems inherent with the previously described fuel cells, thermoelectric conversion cells have be designed. These thermoelectric conversion cells utilize heat to produce a pressure gradient to induce the flow of a reactant, such as molten sodium, across a solid electrolyte. A current is generated as sodium atoms lose electrons upon entering the electrolyte and gain electrons upon leaving the electrolyte. These cell however also suffer from the plugging of the porous electrodes required to pass the sodium ions. Furthermore, the diffusion of the sodium ions through the solid electrolytes has proven to be slow, thereby limiting the amount of current produced by the cell. Lastly, these types of fuel cells operate at extremely high temperatures, typically in a range between 1,200-1,500 degrees Kelvin, making them impractical for many uses.
Another problem associated with thermoelectric conversion cells has been their dependency upon an heat source to enable the operation of the cell. As such, these fuel cells have typically been rather large in size. Furthermore, the requirement of these cells to include a heat source has oftentimes prevented their use in remote area where it would be impractical to locate and operate such, or where it is undesirable to have one notice the physical presence of the cell.
Accordingly, it is seen that a need remains for an electrochemical conversion system that does not require a continuous source of reactant, which does not require an electrolyte which may become plugged over time, which may operate without notice, and which may be operated at relatively low temperatures. It is to the provision of such therefore that the present invention is primarily directed.
In a preferred form of the invention an electrochemical conversion system comprises a first mass of hydrogen absorbent material, a second mass of hydrogen absorbent material spaced from the fist mass of hydrogen absorbent material, a first electrode, a second electrode, a proton conductive membrane positioned between the first electrode and the second electrode, and a supply of hydrogen. The first electrode, second electrode and proton conductive membrane are operably positioned between the first mass of hydrogen absorbent material and the second mass of hydrogen absorbent material. The system also includes a housing containing the first mass of hydrogen absorbent material, the second mass of hydrogen absorbent material, the first electrode, the second electrode and the proton conductive membrane. The housing has a first portion containing the first mass of hydrogen absorbent material and a second portion containing the second mass of hydrogen absorben material. The housing first portion is configured to be implanted into the ground and to thermally transfer heat to and from the first mass of hydrogen absorbent material to the ground. With this construction, the first and second masses of hydrogen absorbent material are in fluid communication with each other through the first and second electrodes and through the proton conductive membrane and the hydrogen may be desorbed by one mass of hydrogen absorbent material and absorbed by the other mass of hydrogen absorbent material while passing through and reacting with the electrodes so as to cause an electric potential difference between the first and second electrodes.